Low molecular weight heparins (LMWHs) are obtained through various methods of chemical and enzymatic depolymerization from clinical-grade unfractioned heparin. As the method of depolymerization varies between products, each LMWHs has an specific fingerprint in its chemical structure and an own distinctive molecular weight profile. Typically LMWHs have a mean molecular weight between 3000 and 7,000 Da. Unlike unfractioned heparin, LMWH chains are too small to form a ternary complex with the thrombin and the antithrombin. Consequently, they exert its anticoagulant activity primarily through inhibition of factor Xa.

The advantages of LMWH over unfractionated heparin are:

1. Better bioavailability: this type of heparin does not bind to proteins or endothelial cells, nor it is neutralized by plasma proteins. Therefore the entire dosage performs the anticoagulant function.
2. More predictable dose-response. Monitoring or dose adjustment is not needed during its administration.
3. Its plasma half-life is longer than that of unfractionated heparin, therefore it can be administered subcutaneously once or twice daily.